The present invention relates to a technology which suppresses noise, in particular, noise caused by an operation of a drive device from an audio signal.
There have been known methods for estimating the noise level of an audio signal containing noise not only in the no-audio period but also in the audio period. Among known methods for estimating the noise level in the audio period is a method of calculating the chronological minimum value or average value of a smoothed signal power spectrum in the audio period as an estimated noise level in the audio period (Japanese Unexamined Patent Publication No. 2009-75536).
For example, noise estimation in the audio period is performed on an audio signal acquired by an image taking apparatus having a function of taking an audio-accompanying moving image. This is because such apparatuses include a drive device for driving components such as a focus mechanism, a zoom mechanism, an aperture mechanism, and a shutter mechanism and, when these mechanisms are driven during image taking, noise caused by the drive operation of the drive device enters an audio signal.
Japanese Unexamined Patent Publication No. 2006-279185, Japanese Unexamined Patent Publication No. 2005-228400, and Japanese Unexamined Patent Publication No. 2008-058343 each disclose a method for suppressing noise caused by a drive operation of a drive device from an audio signal acquired by an image taking apparatus as described above. These methods are intended to perform noise level estimation and noise suppression during the operation period of the drive device.